Alloys and rectifiers made thereof



Oct. l2, 1954 K. LARK-HoRovlTz ETAL 2,691,577

ALLOYS AND RECTIFIERS MADE TIERE'OF' 2 Sheets-Sheet l Original Filed July 13, 1945 INVENTORS. /farar/L-/orou' a. fi?

Oct. l2, 1954 K. LARK-HoRovl-rz l-:TAL

ALLOYS AND RECTIFIERS MADE THEREOF 2 Sheets-Sheet 2 Original Filed July 13, 1945 [Nl 'ENTORS /1 araf/a-Horoz/j BY MIZ/Y Patented Oct. 12, 1954 UNITED y.STATES PATENT IOFF 2,691,577 ICE ALLOYS' AND RECTIFIERS MADE THEREOF Karl Lark-Horovtz and Randall M. Whaley, Lafayette, Ind., assignors to Purdue `Research Foundation, Lafayette, Ind., a corporation of Indiana Original application July 13, 1945, Serial No.

604,744. Divided and this application December31,'1949, Serial No. 136,284

2 Claims.

:ment in alloys of germanium, and more .particularly to rectiersvoffelectricity, `which offer low resistance to current Iiow in one direction therethrough and-high resistance to current ow in the opposite direction, made of such alloys. In the detailed description of our invention Afollowing hereinafter, it will be observed that .several of the elements which may be combined with germanium are not metals so that the resultant materials are not alloysin the common meaning of the word. However, for purposes of theA present disclosure, it is to .be understood that `the word alloy of germanium as used herein, means yto includea union of two ormore elements, one of which is germaniumand the other or others being metals, non-metals, or gases, and the combination of which exhibits electrical properties such as are found in metals and semiconductors.

The known contact rectifiers, i. e., rectiers comprising suitable metal electrodes, and a semiconductor have at least one of the following disadvantages:

1. Inability to withstand in continuous use voltages in the back or high resistance direction Agreater than about volts without permanent injury to the rectifier.

2. Inability to pass suliicient current y,in the forward direction for satisfactory operation of associated apparatus.

3. Low back resistance prohibiting use of the rectifier in high impedance circuits, that is, circuits over about 100,000 ohms.

4. Seriously decreased efficiency in rectifying at frequencies greater than about 1 to 5 megacycles.

5. Capacity too high to allow efficient operation at frequencies greater than about 5 megacycles.

Due to the aforesaid deficiencies of these known contact rectiers, the art turned to widespread use of vacuum tube diodes for rectifying alternating currents. However, vacuum tube diodes, while overcoming certain of the aforementioned disadvantages of the known contact rectiers, in turn have the following disadvantages:

1. Inter-electrode capacities which are seriously objectionable at high frequencies.

2. Low forward direction conductance.

3. Requirement of power for heating a cathode.

4. Require a large amount of space as compared to a contact rectifier.

The germaniumalloys of our present invention may be used as the semi-conductors for rectiers of the contact type, which, according to 2 one embodiment of our invention, possess the following general advantages over known contact -rectiers:

1. Ability to withstand continued operating voltages greater than 10 volts in the back direction, and `some of which are fcapable of withstanding voltages in the back direction -of an order approaching y200 volts.

2.Low .forward resistances, for example, 30 tol00 ohms at one volt. 3. High back resistances, at vabout .4 volts rangingfrom about 10,000 ohms to several megy ohms.

14. May be used with frequencies up tov megacycles and will ystill rectify at v3,000megacyc1es.

5. Provide rectiers of lowcapacity of about micromicrofarad.

6. Less than 50% decrease in .peak back voltage when ambient temperature increases :from

'7. Do not'require power for heating a cath- 1 ode; and

8. .Do not require more space than about that needed fora :common one-half `watt carbon resistor.

.The germanium alloys herein disclosed are all of the class of N-type semi-conductors, i. e., `.semi-'conductors which when made into contact type rectiflers .present a high resistance to current ow across the rectifying contact when the semi-conductor is positive and the contacting metal electrode or Whisker is negative, and a -lowerresistance when the potential is reversed.

The various germanium alloys of our invention -will be described and compared according to the properties they exhibit when made into contact type rectiers. Specic electrical properties hereafter referred to are:

:Peak back: comma- The voltage-current characteristics measured on rectiiiers using the alloys of our invention show'a Avoltage peak in the back or high resistance direction. This peak generally occurs within a range greater than l0 volts and approaching the order of .200- volts. It will 4also appear that all of these rectifiers using alloys yof our invention exhibit a negative resistance 3 impairment of the rectifying contact. As will be described later herein, currents greater than 100 milliamperes are sometimes deliberately passed momentarily in the forward direction to produce improvement in certain Contact characteristics.

The N-type semi-conductors of our invention comprise germanium having small amounts of one of the following elements or certain combinations thereof alloyed therewith:

Copper and silver oi column I of the periodic table;

Magnesium, calcium, Zinc, strontium, cadmium, or barium of column II of the periodic table;

Titanium, tin, or lead, of column IV of the periodic table;

Nitrogen, vanadium, columbium, tantalum, or

bismuth of column V of the periodic table;

Chromium or uranium of column VI of the periodic table;

Cobalt, nickel, or palladium of column VIII of the periodic table.

N-type semi-conductors of germanium may also be formed by alloying, small amounts of, for example, phosphorous, arsenic, or antimony with germanium, but in rectiers using such semiconductors it has been found that excessive currents pass at voltages greater than about 3 to l0 volts in the back direction which permanently injure the rectifying contact. It will be understood therefore that our present invention only relates to semi-conductors of the N-type which exhibit high back voltage characteristics in excess of at least i volts, and does not concern all N-type semi-conductors consisting of an alloy of germanium, as for example, the group last referred to.

Other features and advantages of our invention will appear from the detail description.

Now, in order to acquaint those skilled in the art with the manner of making alloys in accordance with our invention, and the utilization thereof as rectiers of electricity, we shall describe in connection with the accompanying drawings and the tables following hereafter certain of the processes used in making the alloys which lie within our invention.

In the drawings:

Figure l shows the voltage-current characteristic curves of several rectifiers using certain of the alloys of our invention, which curves are not to be taken as typical of given alloys but merely to represent the type of characteristic exhibited by such alloys in general.

Figure 2 is a graph illustrating the electrical characteristics of rectiers using different types of surfaces on one alloy of our invention.

Figure 3 is a sectional view of a rectifier, the semi-conductor of which comprises an alloy of our present invention.

Each alloy represented by the curves of Figure l. is designated by a code number. The latter part of each code denotes the amount in atomic percent of the particular element or elements added to germanium to produce that alloy. No atomic percentage figures for the addition of nitrogen to germanium are given since it is difficult to determine accurately the amount or number of nitrogen atoms alloyed with the germanium.

In the following Table I there are set forth minimum, average, and maximum values of peak back voltage and forward current obtained on rectifying contacts using certain germanium a1- loys which we have made in accordance with the general procedure to be described later. The amount of the added element alloyed with germanium is set forth for each melt in atomic per- 4 cent, i. e., the proportionate number of atoms in percent of the elements added to the total number of the atoms of germanium and added elements present. For purposes of adequately setting forth and claiming our invention, these additions to germanium are to be understood as being included in the term Group A used hereinafter. Substantially al1 melts in which the addition consisted of a single element made to date in accordance with our invention are contained in Table I. It will be observed from that table that a large number of melts with certain added elements were prepared and it will be understood that the results given are the average results of all of the melts in each instance. It is to be understood, however, that the spread or range of values given in connection with each of the elements added to germanium might not be true for any particular melt of such addition agent. Characteristics for rectifying contacts on any given alloy will lie somewhere within the range given. Further, all points on any given alloy listed in Table I and Table II, referred to hereinafter, will not exhibit the same electrical characteristics. Points may be found on each of the alloys disclosed at which the peak back voltages, back resistances, or for- Ward currents lie in the lower regions of the ranges given above for these values. Also on the same surface of each alloy other points of ccntact may usually be found with electrical characteristics which lie toward the upper limit of the ranges above set out. However, as will later be discussed in more detail, some of the alloys are of greater uniformity than others with respect to rectication characteristics.

TABLE I Additions to germanium [In atomic per cent] Forward Current Peggeyctgolt at one volt D. C. Additions and percentages (MHmmperes) Min. Ave. Max. Min. Ave. Mar.

. l5 50 125 7 13 19 Gd: .90, .3G 20 50 105 8 l2 16 Ca: 2.0, 1.35, .80, .50, .50,

.80, .80, .80, .80, .8O 25 150 5 15 25 Cr: .045, .50 g 5 15 25 5 15 25 0o: .50 20 30 35 10 15 2O Cb: .20, .43, .045... 15 25 40 5 15 l10 Cu: .60, 2.00, .42, .19, .34,

.35 25 70 135 l l5 25 Me: 3.0, 3.0 i, l0 60 115 2 10 20 Nit 1.25, .10, .50, 1.0, 1.0,

1.0, 1.0,-1.0 20 50 90 7 15 30 N2: Solidfled in Ni at pressures of2, 1S, 600, and 700,

H 20 80 1GO 7 10 25 30 65 110 5 15 25 25 40 8O 7 10 20 25 75 150 2 l5 30 10 30 I0 3 7 15 20 25 50 2 5 20 l0 25 l 65 10 25 40 25 50 100 5 12 20 In Table II below there are set forth the melts in which two elements have been alloyed .with germanium. The additions of these combinations of elements are also set forth in atomic percent as previously defined. It will be understood that the alloys set forth in this table are also to be included in the term Group A above referred to for purposes of claiming our present invention. The peak back voltages and the forward currents at one volt of rectiiiers made of these alloys are also set forth 1n th1s table,

TABLE II M elts of more than one addztzon to germanium [In atomic per cent.]

Peak 13,515,201 Fitfetie age S Additions and Percentages (Mmiampems) Min Ave. Max. Min. Ave. Max

.20 B1, .20 su 20 25 50 s 15 25 .35 Cu, .70 sn.. 25 40 150 15 20 30 .21 ou, .05 s 50 s0 15 22 50 .21 Cu, .95 su 15 40 05 15 30 00 .so oa, .30 sn 50 70 110 5 14 20 .50 sr, .30 su. 50 7o 100 6 15 35 .50 N1, .50 sr... 55 75 100 0 30 30 .50 Pd, .50 sr 35 55 00 s 15 25 .50 Pd, .50 sr 35 50 95 5 12 2o .50 N1, .10 sr... 39 50 05 s 15 25 .50 N1, .50 Mg. 50 75 12 20 40 .50 Ni, .30 C 45 75 10 20 55 '.50 N1, .50 sr... 30 40 50 9 12 14 .50 N1, .50 sr.. 15 25 35 10 15 20 .50 N1, 1.00 sr 50 90 150 10 15 25 1.00 es, 1.00 sr. 10 50 50 15 20 25 .50 Mg, .50 sr- 10 30 45 10 20 40 1.00 N1, .50 sr 05 100 7 10 18 1.20 sn, .s2 sr 20 100 155 e 15 19 1.20 su, .32 sr 15 00 100 0 10 15 1.00 N1, .50 su 30 70 110 15 20 25 1.00 N1, .50 su 15 50 90 1 e 19 .s0 35 75 140 2 7 9 .so 15 40 75 3 5 7 '.10 sn, .40 oa... 7o 100 175 s 15 2A The` germanium alloys of our invention may be prepared in all cases except for the germaniumy nitrogen alloy, by melting pure germanium with the desired alloying element or combination of elements in either a high vacuum of the order of 10g5 mm. mercury at about 1000 C. or in an atmosphere of helium. Precaution should be taken to prevent the accidental introduction of unknown and perhaps detrimental impurities into the melt from sources such as the crucible or boat in which the ingredients are disposed for melting, the furnace itself, or some material volatilized in the furnace. Alloying germanium with nitrogen may be effected by melting the germanium in an atmosphere` of nitrogen which may be either purified nitrogen or nitrogen direct from a commercial cylinder. The germanium is melted in nitrogen at pressures ranging from about 2 mm. to '760 mm. Hg at a temperature of 1000 to 1050" C. Good results appear to be independent of pressure and melts prepared within the above range. of pressures were all satisfactory.

The germanium successfully used for these alloys had purity approaching 100%, and electrical resistivity greater than about one ohm cm. The germanium which we have successfully alloyed with other elements to form the alloys listed in Tables I and II was prepared from GeOz obtained from the Eagle-Picher Lead Company of Joplin, Missouri. The oxide was reduced in an atmosphere of commercial hydrogen at temperatures of 650 to 700 C. overa period of three to four hours. The oxide reduced in this manner leaves the germanium metal in the form of a gray-green powder- Which is then alloyed with another ele- 6 ment or elements in the manner and proportions described.

The aforesaid melts ofl germanium and the added element orelements were held in the molten state long enough to allow mixing of the constituents, and it has been found that about 5 to l5 minutes is sucient for this purpose. Usually ingredients to form meltsof about ve toy Six grams each were used in proportions above set forth in detail. After the constituents had been allowed to mix, the melts were allowed to solidify and cool which was accomplished either by immediately removing heat or by controlled cooling apparatus. In certain cases the uniformity of the melt is affected by the manner in which it is cooled. These variations will be discussed later.

A specific melt in accordance with our invention was prepared as follows:

Pure GeO2 was reduced in hydrogen at atmospheric pressure for about three hours at 650 'to 700 C. Six grams of pure germanium powder so obtained were then placed in a porcelain crucible together with small flakes of'pure tin amounting to 25 milligrams or about 0.8 atomic percent of tin.

The Crucible and contents were then placed inside a graphite cylinder used as a heater in the high frequency field of an induction furnace, and lowered in a vertical quartz tube which was then evacuated and maintained at a pressure of about 10-5 mm. mercury. Power was then applied to the external coil of the induction furnace to melt the germanium and hold it molten for about 5 minutes. The melt was then allowed to cool by merely turning oif the power to the coil. Thereafter wafers were cut from the alloy, andwere soldered with soft-solder to a suitable metal eleetrede to produce a very low resistance non-rectifying contact with one face of the wafer. The exposed face was then ground with 600 mesh alumina and etched for 2 minutes with an etching solution consisting essentially of HNOS, HF, Cu(NOe)2 and water in proportions to be later described herein. These wafers were then assembled in suitable cartridges each provided with a conventional metal electrode or Whisker which was used to contact the alloy surface. Across the rectifying contact thus produced we obtain the electrical characteristicsdescribed above.

As mentioned in the above specific example, the surfaces of these alloys flat and then etched in a manner to be described in detail. However, as hereinafter related, the etching of the alloy surfaces is not essential since, for example, by breaking open a melt, points may be found which exhibit the aforementioned eleotrieal rectifying characteristics. Such brel-:en surfaces present geometrically irregular faces which introduce some difficulty in assembly of the rectiiiers. Thus, grinding the alloy surface flat and etching it appears to be the most feas-- ible manner of producing the rectiers in the commercial practicing ofour invention. 'A

From the above Table I it will ce observed that the majority of experimental work conducted in the development of our invention has'been with the alloy germanium-tin. In connection with our experimental work with tin it hasy been found that above 0.1 atomic percent of tin content, the amount of tin added is notcr-iticai. Germanium containing above about 0.1 percent tin usually shows tin separated out, both at internal grain boundaries and on the outer surfaces. Insome melts containing tin in excess of'0.1 atomic percent, ductile layers ofthis tin-rich material were are usually ground frequently observed, particularly inthe lower resions of the melt. In this connection we wish to observe that in making the germanium-tin alloys it is desirable in producing the melt that the boat or crucible in which the elements are contained be gradually removed from the hot furnace region. This will produce more uniform alloys, particularly if the melt is so removed that the toll region of the melt is the last part to cool. It appears that germanium becomes saturated at about 0.1 percent tin under the melting and cooling conditions used. However, in our experimental Work larger amounts of tin were added in order to observe if such solubility depended upon the amount of tin available; more tin merely segregated. At i7 atomic percent addition of tin, the entire melt was interlaced with tin-rich veins which had metallic low resistance ohmic con ductivity.

With bismuth additions it is difficult to control the amount of bismuth actually remaining in the germanium during the melting cycle. A considerable fraction of the bismuth volatilizes so that quantities added have little relation to the quantities actually remaining in the melt. However, the results indiccated in Table I in connection with bismuth were obtained by the addition of bismuth to the extent there indicated.

After the melts have been made as above described they are suitable for use as rectifiers of electricity by simply making contact with the surfaces of such alloys with suitable electrodes or whiskers. In most of our experimental work a mil tungsten whisler sharpened electrolytically With a tip diameter of less than 0.1 mil was used as one electrode or Whisker, the other electrical contact usually being made by soldering the alloy to a suitable conductor. However, tests have shown that the peak back voltages of rectiflers made from the alloys of our invention are little affected by the metal of which the Whisker is made. Whiskers made of the following metals have been tried and only very slight deviations were noted over a large number of points of contact with the alloys of our invention: Mn, Pt, Ta,

Ni, Fe, Zn, Mo, W, Au, Cu, Ag, Zr, Pt-Ir, and Pt-Ru. lt appears therefore, that choice of a Whisker material may be determined on the basis of requirements other than the peak back voltage on rectiiiers using the alloys. rIhese electrodes or whiskers may have contact with the surfaces of the alloys as formed upon solidiiication, or on surfaces exposed by breaking the melt. As mentioned above, however, it is desirable to grind and etch the surface. Thus in one method of producing reati-fiers using the alloys of our invention, the melts, which usually were of pellet form 5 to lil millimeters thick, may be cut into thin plates or slabs and a surface thereof ground with a suitable abrasive such as Sil@ mesh alumina (AlzOs). rlhe abrasive used is not critical in that it has been found that other abrasives such as CrzOa, MgO, VazOa, SnOz, ZnO and l-- paper are equally satisfactory. may then be followed by a further grinding step with line emery paper although this grinding step may be eliminated, if desired, without substantially alteringr the final product. The surface of the plate or slab is then etched with a suitable etching solution which in one modification of our invention has the following approximate composition;

4 parts by volume hydrofluoric acid (48% reagent) 4 parts by volume distilled water 2 parts by volume concentrated nitric acid S 200 milligrams Cu(NO3)2 to each l0 tion.

Such a solution will satisfactorily etch the surface of the plates or slabs in about 1 to 2 minutes at room temperature and may be applied with either a swab or by immersing the surface in the solution. This etching is not particularly critical but care should be taken not to unduly extend theetching since then a high polish is produced which may impair the performance of the alloy.

We have also found that other types of etches may be used effectively on the germanium alloys of our invention in addition to the etching above described.l Modified etching solutions and procedures are as follows:

A solution consisting approximately of 1 gram stannyl chloride in 50 cc. of H2O may be used as an'electrolytic bath for etching the alloy surfaces. Immersing the alloy as the anode in this solution will result in satisfactory etching Within about Vll/zniimites at about 21/2 volts applied.

An alternative modilicationV of an electrolytic etching solution may comprise 5 parts concen-V trated HNO3 and 5G parts H2O by volume. .Using the alloy as the anode for about 1% minutes at 1y to 2 volts will result in a satisfactory etch.

Reference may now be had to Figure 2 of the drawings illustrating the effect of etching of one of the alloys of our invention. The alloy selected to illustrate the effect of etching is identified asj melt 24 P-OUlSS-.Zsn This melt as appears from the aforesaid designation constitutes .25 atomic percent tin. The curve identified by reference numeral I illustrates the electrical characteristic of the germanium-tin alloy above identied in which the surface was ground with 60G A1203 but'not etched. The curve indicated bythe reference numeral 2 illustrates the electrical characteristics which were obtained on a freshly broken surface of an alloy of the above composition but which surface has not been etched. Curve member 3 illustrates the electrical characteristic of a surface ground with 60() .A1203 and then etched in accordance with the manner first described.

The curve indicated by the reference numeral ll illustrates electrical characteristics of another point on the alloy after etching as described in connection with curve 3, the curves -3 and d representing the best and poorest performances, respectively, of the particular germanium tin alloy above identified, after etching. It is to be observed that in this graph the voltage scale in the forward direction is there expanded by a factor of l0 as compared to the voltage scale indicating the high back voltage characteristics of the alloys of our invention. As indicated, the currents are given in milliamperes.

It will be observed from an examination of Figure 2 that the electrical characteristics of a cc. of solurectifier using a broken surface exhibit high back voltages and forward conductances within the range of values obtained when using a ground and etched surface. However, such broken sur faces are shiny and geometrically irregular so that the Whisker tends to skid which is undesirable in assembling permanent rectifier units. From Figure 2 it is apparent that the high back voltage and high back resistance properties are inherent in the alloys and that the etching is effective for restoring such properties after grinding. Further, we have discovered that natural surfaces formed when solidifying the alloys in vacuum wilLAif not contaminated or otherwise assis-w rwill affected by grinding, gi 'e high back rouages and high back resistanees when mounted and tested in air.

For certain applieations of these rectifiers it is desirable that they have back resistances exceeding 'one r'negohm at about 5 volts. Using the procedure described above will occasionally produce such high back resistances. However, we have found that a substantial and permanent increase in the back resistance can be e'ected by applying power 'overloads across the contact, for short intervals of time, eachof length about 1/4 to lsecond or longer. The power treatment can be elected with the use of 4either alternating or direct current. By gradually increasing the voltage applied, and hence the current passed by the `contact during successive pulses, an optimum value can be found to produce themaximumbact: resistance for a given contact. For direct current treatment in the iorward direction such optimum current values range from about 20G to 800 milliamperes For alternating power treatment the optimum values of forward peak current range from about 300 milliamperes to 1000 milliamperes. One can apply such alternating current treatment simply by connecting the rectier in series with a current limiting resistance and the secondary of a transformer. Depending upon the size of this current limiting resistance, values of to 40 ohms have been used, voltage pulses ranging from 7 to 60 volts across the rectier and resistance serve to yield the maximum increase in back resistance.

`Table III shows the permanent effects of such power treatment upon a few typical rectiers yusing alloys of our invention and prepared as described. It will be seen from the table that the most significant eiect of the power treatment is the increase in the back resistance as measured at about 4.5 volts. This resistance is increased by factors ranging from about 10 to 50 times the values measured before treatment. Relatively minor increases of 10 to 20 percent are eiected on the peak back voltage. Forward currents at one Volt are in general descreased by amounts ranging from 10 to 50 percent.

TABLE III Eects of power treatment [Values before power treatment are followed in brackets by values after power treatment] Forward Peak Back Current Back Resistance Alloy used in Rectifier Voltage voeg; (ol 1 at 1 5 Vous (volts) amperes) (megohms) It has been demonstrated above that the high -back vol-tage, high Noack resistance, and good forward conductance properties disclosed are inherent in the germanium alloys of our invention. Modifications of surface treatments or power treatments as Ydescribed above will, however, vary the magnitude of the'se properties within certain general limits. For example, on a given allo-y surface, variations in surface treatment and power treatment may be expected to vary the average peak back voltage by a factor of about 2, the average forward current by a factor of about 2, 'and lthe average back resistance by factors up to 50. It will be noted that the `back resistance is the property most sensitive to variations in treatment, particularly to power treatment.

The following Table IV summarizes, on the basis of all melts made in experimental work conducted un'der our invention, the approximate gur'es of the minimum, average, and maximum values of y'peirk back'voltage and forward current at one volt which might be expected on the germanium alloys consisting of :the addition of a single element.

TABLE IV f 'Forward Current Vgaaelglls) iinglnei er?? Auoy P s Min. Ave. Max. Min. Ave. Max.

25 75 150 2 15 30 20 8O 160 7 10 25 25 75 150 5 15 25 25 75 150 5 10 25 20 50 90 7 15 30 25 50 100 5 12 20 25 70 135 1 l5 25 30 65 110 5 15 25 10 50 100 2 10 20 20 50 105 5 12 15 15 50 125 7 13 20 15 40 100 l0 l5 30 25 40 80 7 10 20 10 30 70 3 7 15 20 30 35 10 15 20 20 40 70 3 15 30 l5 40 75 1 5 40 15 25 40 5 15 40 10 25 65 10 25 40 20 25 50 2 5 20 5 15 25 5 15 25 It will appear from the above table that the ranges of values for the better alloys appear to be quite similar. Diiferences enter in the manner in which ythe values, within the ranges indicated, are concentrated. For example, the nitrogen alloys can usually be expected to have 70 to 90 percent of back peak voltages over 60 volts. Values on tin melts are more uniformly spread within the range of the limits given above. For the tin melts approximately 50% of the points on the surfaces thereof will have voltages above 60 volts. It appears that the pure germanium alloyed with tin or melted in an atmosphere ci nitrogen represents the most advantageous alloy.

Following them, alloys of .pure germanium with calcium, strontium or nickel appear to be in order. It is to ibe understood, however, that one skilled in the art working vwithin the range of the alloys herein disclosed will readily be able to produce alloys having high back voltage and resistance characteristics and good forward conductances.

In Figure 3 of the drawings we have shown one type of rectifier in which our invention may Abe embodied. In the form of the device there is shown a wafer 5 which may be of any of the germanium alloys above disclosed mounted to have a low resistance non-rectifying contact with a. metal electrode member ii. An electrode or Whisker l is connected at one end to an electrode supporting member 8 with the end of the Whisker in contact with the surface of the germanium alloy wafer 5. The standard 9 provides lfor mounting of the members supporting the wafer 5 and electrode or Whisker 'I in insulated relation. The rectifier contemplated by our invention may be of various forms, the only critical constructional feature being that the germanium alloy Wafer comprising the semi-conductor, and the Whisker for contacting the surface of the wafer being arranged and supported so that one end of the Whisker engages the semi-conductor surface. It is understood that suitable lea-ds are connected to the Wafer or semi-conductor and to the Whisker or metal electrode so that the device may have application in any desired circuit for use in the rectication of current.

While We have disclosed what we consider to be the preferred embodiments of our invention, it will be understood that various modifications may be made therein Without departing from the spirit l and scope of our invention.

We claim:

1. An alloy having semi-conducting `properties and consisting essentially of germanium and titanium in an amount up to 0.5 atomic percent.

2. A method of making a semi-conductor comprising purifying germanium until it has a purity of at least 99 percent and a resistivity of at least about l ohm cm. and then alloying with the germanium a small predetermined percentage of titanium in an amount up to about 0.5 atomic percent, the alloying being carried'out by melting the constituents in an inert atmosphere.

References Cited in the le of this patent l UNITED STATES PATENTS Number Name Date y2,472,770 Helterline June 7, 1949 2,530,110 Woodyard Nov. 14, 1950 OTHER REFERENCES 

1. AN ALLOY HAVING SEMI-CONDUCTING PROPERTIES AND CONSISTING ESSENTIALLY OF GERMANIUM AND TITANIUM IN AN AMOUNT UP TO 0.5 ATOMIC PERCENT. 